Mathematica function with multiple IF[] conditionals

I have here a complicated bit of code that is not pretty nor easy to follow, but it represents a simplification of a larger body of code I am working with. I am a Mathematica novice and have already received some help on this issue from stackoverflow but it is still not solving my problem. Here is the code for which I hope you can follow along and assume what I am trying to get it to do. Thanks to you programming whizzes for the help.

a[b_, c_] = -3*b + 2*c + d + e + f;

g[b_, c_] := If[a[b, c] < 0, -3*a[b, c], a[b, c]开发者_运维问答];

h[T_, b_, c_] = (T/g[b, c]);

i[h_, T_, b_, c_] := If[h[T, b, c] > 0, 4*h[T, b, c], -5*h[T, b, c]];

j[b_, c_] := If[a[b, c] < 0, 5*a[b, c], 20*a[b, c]];

XYZ[h_, T_, i_, g_, j_, b_, c_] = T*i[h, T, b, c]*g[b, c] + j[b, c]

rules = {a -> 1, b -> 2, c -> 3, d -> 4, e -> 5, f -> 6, T -> 10};

XYZ[h, T, i, g, j, b, c] //. rules

Preserving as much of your code as possible, it will work with just a few changes:

a[b_, c_] := -3*b + 2*c + d + e + f;

g[b_, c_] := If[# < 0, -3 #, #] & @ a[b, c]

h[T_, b_, c_] := T / g[b, c]

i[h_, T_, b_, c_] := If[# > 0, 4 #, -5 #] & @ h[T, b, c]

j[b_, c_] := If[# < 0, 5 #, 20 #] & @ a[b, c]

XYZ[h_, T_, i_, g_, j_, b_, c_] := T*i[h, T, b, c]*g[b, c] + j[b, c]

rules = {a -> 1, b -> 2, c -> 3, d -> 4, e -> 5, f -> 6, T -> 10};

XYZ[h, T, i, g, j, b, c] /. rules

(* Out= 700 *)

1. If statements are again externalized, as in the last problem.

2. all definitions are made with SetDelayed (:=), as a matter of good practice.

3. The presumed error T - 10 in your rules is corrected to T -> 10

Notice that again ReplaceRepeated (//.) is not needed, and is changed to /.

We still have a nonsensical rule a -> 1 but it does not cause a failure.